The present disclosure relates to semiconductor fabrication, and more specifically, to methods and semiconductor devices having contact openings with double barrier layer sets.
During semiconductor fabrication, contacts are used to vertically electrically connect different devices in a semiconductor device. As shown in FIG. 1, the process may include creating a doped or implanted region 10 in a surface 12 of a semiconductor substrate 14, and forming an interlayer dielectric layer 16 thereover. A contact opening 18 is then formed by optical lithography through interlayer dielectric layer 16 to the doped or implanted region 10. A pair of layers 20, 22 may be provided in contact opening 18 to prevent metal migration into interlayer dielectric layer 16, e.g., of tungsten. Titanium layer 20 is used to form silicide to form an ohmic contact, and titanium nitride barrier layer 22 acts as a barrier to migration. A typical approach provides titanium layer 20 deposited into contact opening 18, and titanium nitride barrier layer 22 thereover to protect underlying titanium layer 20 from fluorine attack during later tungsten deposition to form the contact. More particularly, a later chemical vapor deposition step oftentimes uses tungsten fluoride gas that upon decomposition forms the tungsten fill for remaining portion 28 of contact opening 18. Prior to tungsten formation, an anneal 24 is performed to create titanium silicide region 26 at the junction of titanium layer 20 and semiconductor substrate 14, i.e., at doped or implanted region 10. One challenge with this process is the high temperature anneal 24 (e.g., at 800° C.) degrades titanium nitride barrier layer 22. More particularly, the high temperature: changes the composition of the titanium nitride by dissolution of the nitrogen from the titanium nitride into titanium layer 20, and creates thermal expansion of titanium layer 20 (see arrows) that creates cracks in titanium nitride barrier layer 22. The cracks make titanium nitride barrier layer 22 ineffective at protecting titanium layer 20 during later formation of tungsten in remaining portion 28 of contact opening 18. During tungsten fluoride chemical vapor deposition to form the tungsten fill, growth defects (not shown) (known as volcano defects) may form in the contact due to the reaction of the fluorine and titanium through the degraded titanium nitride barrier layer.